System and process for production of aniline and toluenediamine

ABSTRACT

A method for producing aniline or toluenediamine is disclosed which comprises forming a dispersion comprising hydrogen gas bubbles dispersed in a liquid medium comprising either nitrobenzene or dinitrotoluene, wherein the hydrogen gas bubbles have a mean diameter less than 1 micron; and subjecting the dispersion to hydrogenation reaction promoting conditions comprising pressure less than about 600 kPa and temperature less than about 200° C., whereby at least a portion of the nitrobenzene or dinitrotoluene is hydrogenated to form aniline or toluenediamine, respectively. A system for carrying out the method is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application which claims the benefit under 35 U.S.C. §121 of U.S. patent application Ser. No. 12/141,196, filed Jun. 18, 2008, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 60/946,493 filed Jun. 27, 2007, and U.S. Provisional Patent Application No. 60/946,469 filed Jun. 27, 2007, the disclosures of each of which are hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

TECHNICAL FIELD

The present invention generally relates to the gas-liquid phase catalyzed hydrogenation of nitrobenzene or methyl dinitrobenzene (dinitrotoluene) to produce the corresponding aromatic amines aniline or toluenediamine, respectively. More particularly, the invention relates to apparatus and methods for producing those aromatic amines, which employ high shear mixing of the reactants.

BACKGROUND

Aniline is widely used in the production of methylene diphenyl diisocyanate (MDI), a key intermediate for polyurethanes and automotive plastics, and is used to produce antioxidants and vulcanization accelerators for rubber, and as an intermediate in the production of herbicides, pesticides, dyes and pigments, among many other uses. Today it is typically produced by catalytic hydrogenation of nitrobenzene, or less commonly, by amination of phenol. Catalytic hydrogenation of nitrobenzene is highly exothermic, having a heat of reaction of about 130 kilocalories per mol. The reaction is carried out commercially in the presence of excess hydrogen in both the vapor phase and the liquid phase. Vapor-phase processes typically employ either fixed-bed or fluidized-bed reactors. Catalysts of palladium or copper on activated carbon or alternate support, often in combination with other metals selected from the group consisting of lead, vanadium, phosphorous, and chromium as modifiers/promoters have proven to be effective for vapor-phase hydrogenation. High activity and selectivity have been obtained with these catalysts. Hydrogenation of nitrobenzene in the liquid phase has been performed with slurry or fluidized-bed reactors. Operating conditions are typically a temperature in the range of from about 90° C. to about 200° C. and pressure in the range of from about 100 kPa to about 600 kPa. In some cases, the liquid phase process utilizes an excess of aniline as the reaction solvent and removes heat produced via the reaction by allowing the reaction mixture to boil off at a reaction pressure usually less than 100 kPa. One catalyst that has been used for the liquid process is finely divided nickel on diatomite. One continuous liquid-phase hydrogenation process is carried out in a plug-flow reactor with a platinum-palladium catalyst on a carbon support, with iron as modifier. The modifier is used to provide good catalyst life, high activity, and protection against aromatic ring hydrogenation.

Toluenediamine (TDA) exists in several isomeric forms. The TDAs are large-volume intermediates used in the production of a wide variety of industrial and consumer products, including explosives (TNT), dyes and plastics. The mixture of 2,4- and 2,6-isomers is used predominantly as an intermediate in the manufacture of toluene diisocyanate. Commercial mixtures of 2,3- and 3,4-isomers, as well as the 2,4- and 2,6-isomers, are used as co-reactants or as raw materials in the manufacture of urethane products, dyes, corrosion inhibitors, and rubber antioxidants. The most commonly marketed isomers and isomer mixtures are 2,4-TDA, 3,4-TDA, m-TDA (an 80:20 or 65:35 mixture of the 2,4- and 2,6-isomers), and o-TDA (3,4-, 2,3-isomers, as 60:40 mixture); 2,5-TDA is also marketed in small quantities. Any single commercial product will contain various levels of the other isomers. TDAs are typically produced from dinitrotoluenes through a liquid phase catalytic hydrogenation process, or by the reaction of iron and hydrochloric acid with the dinitrotoluenes. Byproducts of the reactions include water and organic by-products, which are separated from the TDA product based on their lower or higher boiling points. Most existing processes and production facilities for toluenediamine or aniline are subject to a variety of constraints such as product yield, plant size, energy consumption and mass flow limitations. Accordingly, there is continuing interest in improving the ways that aniline and toluenediamine are produced.

SUMMARY

In accordance with certain embodiments of the invention, a method is provided for producing aniline or toluenediamine, which includes forming a dispersion comprising hydrogen gas bubbles dispersed in a liquid medium comprising either nitrobenzene or dinitrotoluene, wherein the hydrogen gas bubbles have a mean diameter less than 1 micron; and subjecting the dispersion to hydrogenation reaction promoting conditions comprising pressure less than about 600 kPa and temperature less than about 200° C., whereby at least a portion of the nitrobenzene or dinitrotoluene is hydrogenated to form aniline or toluenediamine, respectively. In some embodiments, the gas bubbles have a mean diameter of less than 400 nm.

In accordance with certain embodiments of the present invention, a method is provided for producing aniline, comprising: forming a dispersion comprising hydrogen gas bubbles dispersed in a liquid medium comprising nitrobenzene, wherein the bubbles have a mean diameter less than 1 micron; and subjecting the dispersion to hydrogenation reaction promoting conditions, whereby at least a portion of the nitrobenzene is hydrogenated to form aniline. In some embodiments, the reaction promoting conditions comprise contacting the dispersion with a hydrogenation catalyst. In some embodiments, the reaction promoting conditions further comprise a pressure less than about 600 kPa and a temperature less than about 200° C.

Also provided in accordance with certain embodiments of the invention is a method for producing toluenediamine, comprising: forming a dispersion comprising hydrogen gas bubbles dispersed in a liquid medium comprising dinitrotoluene, wherein the bubbles have a mean diameter less than 1 micron; and subjecting the dispersion to hydrogenation reaction promoting conditions, whereby at least a portion of the dinitrotoluene is hydrogenated to form toluenediamine. In some embodiments, the reaction promoting conditions comprise contacting the dispersion with a hydrogenation catalyst. In some embodiments, the reaction promoting conditions further comprise a pressure less than about 600 kPa and a temperature less than about 200° C.

Also provided in accordance with certain embodiments of the invention is a system for production of aniline from nitrobenzene or for producing toluenediamine from dinitrotoluene. The system comprises at least one high shear mixing device configured for producing a dispersion of hydrogen gas bubbles in a liquid medium comprising either nitrobenzene or dinitrotoluene, wherein the dispersion has a mean bubble diameter of less than 400 nm; a pump configured for delivering a liquid stream comprising nitrobenzene or dinitrotoluene to the high shear mixing device; and a vessel configured for receiving the dispersion from the high shear mixer and for maintaining a predetermined pressure and temperature. In some embodiments, the vessel comprises a hydrogenation catalyst. These and other embodiments and potential advantages will be apparent in the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram of a process for production of either aniline or toluenediamine, according to certain embodiments of the invention.

FIG. 2 is a longitudinal cross-section view of a multi-stage high shear device, as employed in an embodiment of the system of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present methods and systems for the production of aniline and toluenediamine via gas-liquid phase partial oxidation of nitrobenzene and dinitrotoluene, respectively, employ an external high shear mechanical device to provide rapid contact and mixing of chemical ingredients in a controlled environment in the mixing device. The high shear device reduces the mass transfer limitations on the reaction and thus increases the overall reaction rate. For the purposes of this disclosure, “dinitrotoluene” and “toluenediamine” include the corresponding isomers, and mixtures thereof.

Chemical reactions involving liquids, gases and solids rely on the laws of kinetics that involve time, temperature, and pressure to define the rate of reactions. In cases where it is desirable to react two or more raw materials of different phases (e.g. solid and liquid; liquid and gas; solid, liquid and gas), one of the limiting factors in controlling the rate of reaction involves the contact time of the reactants. In the case of heterogeneously catalyzed reactions there is the additional rate limiting factor of having the reacted products removed from the surface of the catalyst to enable the catalyst to catalyze further reactants. Contact time for the reactants and/or catalyst is often controlled by mixing which provides contact with two or more reactants involved in a chemical reaction. A reactor assembly that comprises an external high shear device or mixer as described herein makes possible decreased mass transfer limitations and thereby allows the reaction to more closely approach kinetic limitations. When reaction rates are accelerated, residence times may be decreased, thereby increasing obtainable throughput. Product yield may be increased as a result of the high shear system and process. Alternatively, if the product yield of an existing process is acceptable, decreasing the required residence time by incorporation of suitable high shear may allow for the use of lower temperatures and/or pressures than conventional processes.

System for Production of Aniline or Toluenediamine.

A high shear aniline or toluenediamine production system will now be described in relation to FIG. 1, which is a process flow diagram of an embodiment of a high shear system 1 for the production of aniline by gas-liquid phase hydrogenation of nitrobenzene, or for the production of toluenediamine by gas-liquid phase hydrogenation of dinitrotoluene. The basic components of a representative system include external high shear mixing device (HSD) 40, vessel 10, and pump 5. As shown in FIG. 1, the high shear device is located external to vessel/reactor 10. Each of these components is further described in more detail below. Line 21 is connected to pump 5 for introducing either nitrobenzene or dinitrotoluene reactant. Line 13 connects pump 5 to HSD 40, and line 18 connects HSD 40 to vessel 10. Line 22 is connected to line 13 for introducing dispersible molecular hydrogen. Line 17 is connected to vessel 10 for removal of unreacted nitrobenzene or dinitrotoluene vapor, and other volatile reaction gases. Additional components or process steps may be incorporated between vessel 10 and HSD 40, or ahead of pump 5 or HSD 40, if desired. For example, line 16 may be connected to line 21 or line 13, to provide for multi-pass operation, if desired.

High Shear Mixing Device. External high shear mixing device (HSD) 40, also sometimes referred to as a high shear mixer, is configured for receiving an inlet stream via line 13, comprising liquid nitrobenzene or dinitrotoluene and molecular hydrogen. Alternatively, HSD 40 may be configured for receiving the liquid and gaseous reactant streams via separate inlet lines (not shown). Although only one high shear device is shown in FIG. 1, it should be understood that some embodiments of the system may have two or more high shear mixing devices arranged either in series or parallel flow. HSD 40 is a mechanical device that utilizes one or more generators comprising a rotor/stator combination, each of which has a fixed gap between the stator and rotor. HSD 40 is configured in such a way that it is capable of producing submicron (i.e., less than 1 micron in diameter) and micron-sized bubbles in a reactant mixture flowing through the mixer. The high shear mixer comprises an enclosure or housing so that the pressure and temperature of the reaction mixture may be controlled.

High shear mixing devices are generally divided into three general classes, based upon their ability to mix fluids. Mixing is the process of reducing the size of particles or inhomogeneous species within the fluid. One metric for the degree or thoroughness of mixing is the energy density per unit volume that the mixing device generates to disrupt the fluid particles. The classes are distinguished based on delivered energy densities. Three classes of industrial mixers having sufficient energy density to consistently produce mixtures or emulsions with particle sizes in the range of submicron to 50 microns include homogenization valve systems, colloid mills and high speed mixers. In the first class of high energy devices, referred to as homogenization valve systems, fluid to be processed is pumped under very high pressure through a narrow-gap valve into a lower pressure environment. The pressure gradients across the valve and the resulting turbulence and cavitation act to break-up any particles in the fluid. These valve systems are most commonly used in milk homogenization and can yield average particle sizes in the 0-1 micron range.

At the opposite end of the energy density spectrum is the third class of devices referred to as low energy devices. These systems usually have paddles or fluid rotors that turn at high speed in a reservoir of fluid to be processed, which in many of the more common applications is a food product. These low energy systems are customarily used when average particle sizes of greater than 20 microns are acceptable in the processed fluid.

Between the low energy devices and homogenization valve systems, in terms of the mixing energy density delivered to the fluid, are colloid mills, which are classified as intermediate energy devices. A typical colloid mill configuration includes a conical or disk rotor that is separated from a complementary, liquid-cooled stator by a closely-controlled rotor-stator gap, which is commonly between 0.0254-10.16 mm (0.001-0.40 inch). Rotors are usually driven by an electric motor through a direct drive or belt mechanism. As the rotor rotates at high rates, it pumps fluid between the outer surface of the rotor and the inner surface of the stator, and shear forces generated in the gap process the fluid. Many colloid mills with proper adjustment achieve average particle sizes of 0.1-25 microns in the processed fluid. These capabilities render colloid mills appropriate for a variety of applications including colloid and oil/water-based emulsion processing such as that required for cosmetics, mayonnaise, or silicone/silver amalgam formation, to roofing-tar mixing.

An approximation of energy input into the fluid (kW/L/min) can be estimated by measuring the motor energy (kW) and fluid output (L/min). Tip speed is the circumferential distance traveled by the tip of the rotor per unit of time. Tip speed is thus a function of the rotor diameter and the rotational frequency. Tip speed (in meters per minute, for example) may be calculated by multiplying the circumferential distance transcribed by the rotor tip, 2πR, where R is the radius of the rotor (in meters, for example) times the frequency of revolution (in revolutions per minute). A colloid mill, for example, may have a tip speed in excess of 22.9 m/sec (4500 ft/min) and may exceed 40 m/sec (7900 ft/min). For the purposes of this disclosure, the term “high shear” refers to mechanical rotor stator devices (e.g., colloid mills or rotor/stator mixers) that are capable of tip speeds in excess of 5.1 m/sec. (1000 ft/min) and require an external mechanically driven power device to drive energy into the stream of materials to be reacted. For example, in HSD 40, a tip speed in excess of 22.9 m/sec (4500 ft/min) is achievable, and may exceed 40 m/sec (7900 ft/min). In some embodiments, HSD 40 is capable of delivering at least 300 L/h with a power consumption of about 1.5 kW at a nominal tip speed of at least 22.9 m/sec (4500 ft/min).

HSD 40 combines high tip speeds with a very small shear gap to produce significant shear on the material being processed. The amount of shear will be dependent on the viscosity of the fluid. Accordingly, a local region of elevated pressure and temperature is created at the tip of the rotor during operation of the high shear device. In some cases the locally elevated pressure is about 1034.2 MPa (150,000 psi). In some cases the locally elevated temperature is about 500° C. In some cases these local pressure and temperature elevations may persist for nano or pico seconds. In some embodiments, the energy expenditure of the high shear mixer is greater than 1000 W/m³. In embodiments, the energy expenditure of HSD 40 is in the range of from about 3000 W/m³ to about 7500 W/m³. The shear rate is the tip speed divided by the shear gap width (minimal clearance between the rotor and stator). The shear rate generated in HSD 40 may be greater than 20,000 s⁻¹. In some embodiments the shear rate is at least 1,600,000 s⁻¹. In embodiments, the shear rate generated by HSD 40 is in the range of from 20,000 s⁻¹ to 100,000 s⁻¹. For example, in one application the rotor tip speed is about 40 m/sec (7900 ft/min) and the shear gap width is 0.0254 mm (0.001 inch), producing a shear rate of 1,600,000 s⁻¹.

HSD 40 is capable of highly dispersing or transporting hydrogen gas into a main liquid phase comprising nitrobenzene or dinitrotoluene. In some embodiments, HSD 40 comprises a colloid mill. Suitable colloidal mills are manufactured by IKA® Works, Inc. Wilmington, N.C. and APV North America, Inc. Wilmington, Mass., for example. In some instances, HSD 40 comprises the DISPAX REACTOR® of IKA® Works, Inc. Several models are available having various inlet/outlet connections, horsepower, nominal tip speeds, output rpm, and nominal flow rate. Selection of a particular device will depend on specific throughput requirements for the intended application, and on the desired bubble size in the outlet dispersion from the high shear mixer. The high shear device comprises at least one revolving element that creates the mechanical force applied to the reactants. In some embodiments, the high shear device comprises at least one stator and at least one rotor separated by a clearance. For example, the rotors may be conical or disk shaped and may be separated from a complementary-shaped stator. Both the rotor and stator may comprise a plurality of circumferentially-spaced teeth. In some embodiments, the stator(s) are adjustable to obtain the desired gap between the rotor and the stator of each generator (rotor/stator set). Grooves in the rotor and/or stator may change directions in alternate stages for increased turbulence. Each generator may be driven by any suitable drive system configured for providing the necessary rotation.

In some embodiments, the minimum clearance between the stator and the rotor is in the range of from about 0.0254 mm to about 3.175 mm (about 0.001 inch to about 0.125 inch). In certain embodiments, the minimum clearance between the stator and rotor is about 1.524 mm (0.060 inch). In certain configurations, the minimum clearance between the rotor and stator is at least 1.778 mm (0.07 inch). The shear rate produced by the high shear mixer may vary with longitudinal position along the flow pathway. In some embodiments, the rotor is set to rotate at a speed commensurate with the diameter of the rotor and the desired tip speed. In some embodiments, the colloidal mill has a fixed clearance between the stator and rotor. Alternatively, the colloid mill has adjustable clearance.

In some embodiments, HSD 40 comprises a single stage dispersing chamber (i.e., a single rotor/stator combination, a single generator). In some embodiments, high shear device 40 is a multiple stage inline disperser and comprises a plurality of generators. In certain embodiments, HSD 40 comprises at least two generators. In other embodiments, high shear device 40 comprises at least 3 high shear generators. In some embodiments, high shear device 40 is a multistage mixer whereby the shear rate (which varies proportionately with tip speed and inversely with rotor/stator gap) varies with longitudinal position along the flow pathway, as further described herein below.

In some embodiments, each stage of the external high shear device has interchangeable mixing tools, offering flexibility. For example, the DR2000/4 DISPAX REACTOR® of IKA® Works, Inc. Wilmington, N.C. and APV North America, Inc. Wilmington, Mass., comprises a three stage dispersing module. This module may comprise up to three rotor/stator combinations (generators), with choice of fine, medium, coarse, and super-fine for each stage. This allows for creation of dispersions having a narrow distribution of the desired bubble size. In some embodiments, each of the stages is operated with super-fine generator. In some embodiments, at least one of the generator sets has a rotor/stator minimum clearance of greater than about 5.08 mm (0.20 inch). In some embodiments, at least one of the generator sets has a minimum rotor/stator clearance of greater than about 1.778 mm (0.07 inch). In some embodiments the rotors are 60 mm and the stators are 64 mm in diameter, providing a clearance of about 4 mm.

Referring now to FIG. 2, there is presented a longitudinal cross-section of a suitable high shear device 200. High shear device 200 is a dispersing device comprising three stages or rotor-stator combinations, 220, 230, and 240. Three rotor/stator sets or generators 220, 230, and 240 are aligned in series along drive input 250. The first generator 220 comprises rotor 222 and stator 227. The second generator 230 comprises rotor 223, and stator 228; the third generator 240 comprises rotor 224 and stator 229. For each generator the rotor is rotatably driven by input 250 and rotates, as indicated by arrow 265, about axis 260. Stator 227 is fixedly coupled to high shear device wall 255. Each generator has a shear gap which is the distance between the rotor and the stator. First generator 220, comprises a first shear gap 225; second generator 230 comprises a second shear gap 235; and third generator 240 comprises a third shear gap 245. In some embodiments, shear gaps 225, 235, 245 are between about 0.025 mm and 10.0 mm wide. In some embodiments, the process comprises utilization of a high shear device 200 wherein the gaps 225, 235, 245 are between about 0.5 mm and about 2.5 mm. In certain instances the gap is maintained at about 1.5 mm. Alternatively, the gaps 225, 235, 245 are different for generators 220, 230, 240. In certain instances, the gap 225 for the first generator 220 is greater than about the gap 235 for the second generator 230, which is in turn greater than about the gap 245 for the third generator. As mentioned above, the generators of each stage may be interchangeable, offering flexibility.

Generators 220, 230, and 240 may comprise a coarse, medium, fine, and super-fine characterization. Rotors 222, 223, and 224 and stators 227, 228, and 229 may be toothed designs. Each generator may comprise two or more sets of rotor-stator teeth. Rotors 222, 223, and 224 may comprise a number of rotor teeth circumferentially spaced about the circumference of each rotor. Stators 227, 228, and 229 may comprise a complementary number of stator teeth circumferentially spaced about the circumference of each stator. In embodiments, the inner diameter of the rotor is about 11.8 cm. In embodiments, the outer diameter of the stator is about 15.4 cm. In certain embodiments, each of three stages is operated with a super-fine generator, comprising a shear gap of between about 0.025 mm and about 3 mm. For any applications in which solid particles (e.g., catalyst) are to be sent through high shear device 200, shear gap width may be selected for reduction in particle size and increase in particle surface area. In some embodiments, the disperser is configured so that the shear rate will increase stepwise longitudinally along the direction of the flow. The IKA® model DR 2000/4, for example, comprises a belt drive, 4M generator, PTFE sealing ring, inlet flange 25.4 mm (1 inch) sanitary clamp, outlet flange 19 mm (¾ inch) sanitary clamp, 2 HP power, output speed of 7900 rpm, flow capacity (water) approximately 300-700 L/h (depending on generator), a tip speed of from 9.4-41 m/sec (1850 ft/min to 8070 ft/min).

Vessel. Vessel or reactor 10 is any type of vessel in which a multiphase reaction can be propagated to carry out the above-described conversion reaction(s). For instance, a fixed bed catalytic reactor, a continuous or semi-continuous stirred tank reactor, or one or more batch reactors may be employed in series or in parallel. In some applications vessel 10 may be a tower reactor, and in others a tubular reactor or multi-tubular reactor. One or more inlet line 15 may be connected to vessel 10 for receiving any additional reactants or catalyst during operation of the system. If desired, vessel 10 may be connected to line 21 for recycling unreacted nitrobenzene or dinitrotoluene back into HSD 40 via pump 5. Vessel 10 may also include one or more of the following components: stirring system, heating and/or cooling capabilities, pressure measurement instrumentation, temperature measurement instrumentation, one or more injection points, and level regulator (not shown), as are known in the art of reaction vessel design. For example, a stirring system may include a motor driven mixer. A heating and/or cooling apparatus may comprise, for example, a heat exchanger. One or more product lines 16 are connected to vessel 10 for removal and recovery of product.

Heat Transfer Devices. In addition to the above-mentioned heating/cooling capabilities of vessel 10, other external or internal heat transfer devices for heating or cooling a process stream are also contemplated in variations of the embodiments illustrated in FIG. 1. Some suitable locations for one or more such heat transfer devices are between pump 5 and HSD 40, between HSD 40 and vessel 10, and between vessel 10 and pump 5, if system 1 is operated in multi-pass mode. Some non-limiting examples of such heat transfer devices are shell, tube, plate, and coil heat exchangers, as are known in the art.

Pumps. Pump 5 is configured for either continuous or semi-continuous operation, and may be any suitable pumping device that is capable of providing greater than 203 kPa (2 atm) pressure, preferably greater than 304 kPa (3 atm) pressure, to allow controlled flow through HSD 40 and system 1. For example, a Roper Type 1 gear pump, Roper Pump Company (Commerce Ga.) Dayton Pressure Booster Pump Model 2P372E, Dayton Electric Co (Niles, Ill.) is one suitable pump. Preferably, all contact parts of the pump comprise stainless steel, or, if corrosive substances will be pumped, the contact surfaces may be gold plated. In some embodiments of the system, pump 5 is capable of pressures greater than about 2027 kPa (20 atm). In addition to pump 5, one or more additional, high pressure pump (not shown) may be included in the system illustrated in FIG. 1. For example, a booster pump, which may be similar to pump 5, may be included between HSD 40 and vessel 10 for boosting the pressure into vessel 10. As another example, a supplemental feed pump, which may be similar to pump 5, may be included for introducing additional reactants or catalyst into vessel 10. As still another example, a compressor type pump may be positioned between line 17 and HSD 40 for recycling unreacted hydrogen and other gases or vapors from vessel 10 to an inlet of the high shear device.

Production of Aniline or Toluenediamine.

In operation for the catalytic production of aniline from nitrobenzene, or, alternatively, for the independent production of toluenediamine from dinitrotoluene, a dispersible H₂-containing gas stream is introduced into system 1 via line 22, and combined in line 13 with either a nitrobenzene- or dinitrotoluene-containing liquid stream. For ease of reference, the dinitrotoluene isomers are individually and collectively referred to herein as “dinitrotoluene”, although it should be understood that a specific isomer or combination of isomers could be substituted in place of the generic term where the context allows. Likewise, use of the generic term “toluenediamine,” in this disclosure represents each of its isomers, individually and collectively, where the context allows. Alternatively, the hydrogen-containing gas may be fed directly into HSD 40, instead of being combined with the liquid reactant (i.e., nitrobenzene or dinitrotoluene) in line 13. In some embodiments an aliphatic alcohol solvent and/or carbon monoxide is added into line 13 to enhance the hydrogenation process and act as a reaction solvent. The unsubstituted alkyl monoalcohols contain from 1-8 carbon atoms, and, in some cases, 1-4 carbon atoms. Examples include methanol, ethyl alcohol, isopropyl alcohol, butyl alcohol, pentyl alcohol, and mixtures thereof. In many cases, the selected alcohol solvent is methanol. If carbon monoxide is included, especially in the production of toluenediamine, it is used in a relatively small proportion, so that the formation of toluenediamine is effected primarily via the hydrogen reduction of dinitrotoluene.

Pump 5 is operated to pump the liquid reactant through line 21, and to build pressure and feed HSD 40, providing a controlled flow throughout high shear mixer (HSD) 40 and high shear system 1. In some embodiments, pump 5 increases the pressure of the nitrobenzene or dinitrotoluene stream to greater than 203 kPa (2 atm), preferably greater than about 304 kPa (3 atm). In some embodiments the pressure is about 1013 kPa (10 atm).

After pumping, the hydrogen and liquid reactants, and any carbon monoxide or alkyl monoalcohol, are mixed within HSD 40, which serves to create a fine dispersion of the hydrogen gas in the nitrobenzene or dinitrotoluene. In some embodiments it may create a fine mixture, emulsion or dispersion of the reactants. As used herein, the term “dispersion” refers to a liquefied mixture that contains two distinguishable substances (or phases) that will not readily mix and dissolve together. A dispersion comprises a continuous phase (or matrix), which holds therein discontinuous droplets, bubbles, and/or particles of the other phase or substance. The term dispersion may thus refer to foams comprising gas bubbles suspended in a liquid continuous phase, emulsions in which droplets of a first liquid are dispersed throughout a continuous phase comprising a second liquid with which the first liquid is immiscible, and continuous liquid phases throughout which solid particles are distributed. The term “dispersion” encompasses continuous liquid phases throughout which gas bubbles are distributed, continuous liquid phases throughout which solid particles (e.g., solid catalyst) are distributed, continuous phases of a first liquid throughout which droplets of a second liquid that is substantially insoluble in the continuous phase are distributed, and liquid phases throughout which any one or a combination of solid particles, immiscible liquid droplets, and gas bubbles are distributed. Hence, a dispersion can exist as a homogeneous mixture in some cases (e.g., liquid/liquid phase), or as a heterogeneous mixture (e.g., gas/liquid, solid/liquid, or gas/solid/liquid), depending on the nature of the materials selected for combination.

In HSD 40, the hydrogen-containing gas and nitrobenzene or dinitrotoluene are highly dispersed such that nanobubbles and microbubbles of the gaseous reactants, and or, nanodroplets or particles of alcohol, if present, are formed for superior dissolution into solution and enhancement of reactant mixing. For example, disperser IKA® model DR 2000/4, a high shear, three stage dispersing device configured with three rotors in combination with stators, aligned in series, is used to create the dispersion of dispersible hydrogen-containing gas in liquid medium comprising nitrobenzene or dinitrotoluene (i.e., “the reactants”). The rotor/stator sets may be configured as illustrated in FIG. 2, for example. For some applications, the direction of rotation of the generators may be opposite that shown by arrow 265 (e.g., clockwise or counterclockwise about axis of rotation 260). The combined gas and liquid reactants enter the high shear mixer and enter a first stage rotor/stator combination having circumferentially spaced first stage shear openings. In some applications, the direction of flow of the reactant stream entering inlet 205 corresponds to the axis of rotation 260. The coarse dispersion exiting the first stage enters the second rotor/stator stage, having second stage shear openings. The reduced bubble-size dispersion emerging from the second stage enters the third stage rotor/stator combination having third stage shear openings. The dispersion exits the high shear mixer via line 18. In some embodiments, the shear rate increases stepwise longitudinally along the direction of the flow. For example, in some embodiments, the shear rate in the first rotor/stator stage is greater than the shear rate in subsequent stage(s). In other embodiments, the shear rate is substantially constant along the direction of the flow, with the stage or stages being the same. If the high shear mixer includes a PTFE seal, for example, the seal may be cooled using any suitable technique that is known in the art. For example, the reactant stream flowing in line 13 may be used to cool the seal and in so doing be preheated as desired prior to entering the high shear mixer.

The rotor of HSD 40 is set to rotate at a speed commensurate with the diameter of the rotor and the desired tip speed. As described above, the high shear mixer (e.g., colloid mill) has either a fixed clearance between the stator and rotor or has adjustable clearance. HSD 40 serves to intimately mix the hydrogen-containing gas and the reactant liquid (i.e., nitrobenzene or dinitrotoluene). In some embodiments of the process, the transport resistance of the reactants is reduced by operation of the high shear mixer such that the velocity of the reaction is increased by greater than a factor of about 5. In some embodiments, the velocity of the reaction is increased by at least a factor of 10. In some embodiments, the velocity is increased by a factor in the range of about 10 to about 100 fold. In some embodiments, HSD 40 delivers at least 300 L/h with a power consumption of 1.5 kW at a nominal tip speed of at least 22.9 m/sec (4500 ft/min), and which may exceed 40 m/sec (7900 ft/min). In some embodiments, the mixture is subjected to a shear rate greater than 20,000 s⁻¹.

Although measurement of instantaneous temperature and pressure at the tip of a rotating shear unit or revolving element in HSD 40 is difficult, it is estimated that the localized temperature seen by the intimately mixed reactants is in excess of 500° C. and at pressures in excess of 500 kg/cm² under cavitation conditions. The high shear mixing results in dispersion of the hydrogen-containing gas in micron or submicron-sized bubbles (i.e., mean diameter less than 1 micron). In some embodiments, the resultant dispersion has an average bubble size less than about 1.5 μm. Accordingly, the dispersion exiting HSD 40 via line 18 comprises micron and/or submicron-sized gas bubbles. In some embodiments, the mean bubble size is in the range of about 0.4 μm to about 1.5 μm. In some embodiments, the mean bubble size less than 400 nm, in the range of about 200 nm to about 400 nm, or it may be about 100 nm in some cases. In many embodiments, the microbubble dispersion is able to remain dispersed at atmospheric pressure for at least 15 minutes.

Once dispersed, the resulting gas/liquid dispersion exits HSD 40 via line 18 and feeds into vessel 10, as illustrated in FIG. 1. The dispersion may be further processed prior to entering vessel 10, if desired. Hydrogenation of dinitrotoluene to form toluenediamine, or of nitrobenzene to form aniline, will occur whenever suitable time temperature and pressure conditions exist, facilitated by the presence of a suitable catalyst. In this sense hydrogenation could occur at any point in the flow diagram of FIG. 1 if temperature and pressure conditions are suitable. A discrete reactor is usually desirable, however, to allow for the presence of a fixed catalyst, increased residence time, agitation and heating and/or cooling. When a fixed bed catalyst is utilized, the reactor becomes the main location for the hydrogenation reaction to occur due to the presence of catalyst and its effect on the rate of hydrogenation. The catalytic reactor may also be operated as a slurry reactor, trickle bed reactor, fluidized bed reactor, bubble column or other suitable reactor configuration. In some applications, the incorporation of external high shear mixer 40 will allow the operation of trickle bed reactors as slurry reactors, for example.

Any of a variety of catalysts that are known for promoting these types of reactions may be employed. It is generally preferred to employ metallic catalysts including mixtures comprising such catalysts. These catalysts may be pelleted, granular or powdered, although for slurry systems the powdered form is preferred, such as having a particle size from about 2 to about 400 microns. For fixed bed systems catalysts may be either supported on a carrier. Some of the useful metallic catalysts which may be employed, together with references to their preparation, are disclosed in U.S. Pat. No. 3,232,989 (Graham et al.). A group of catalysts for production of toluenediamine is nickel, platinum, palladium and mixtures thereof, one of which is Raney nickel. In some cases, the vessel 10 is charged with catalyst and, if required, the catalyst is activated according to procedures recommended by the catalyst vendors.

Catalyst may be introduced into the vessel via line 15, as an aqueous or nonaqueous slurry or stream, or it may be present in vessel 10 as a fixed bed, for example. As a result of the intimate mixing of the H₂ and nitrobenzene or dinitrotoluene reactants prior to entering vessel 10, some portion of the chemical reaction may take place in HSD 40, with or without the presence of a catalyst. Accordingly, in some embodiments, reactor/vessel 10 may be used primarily for heating and separation of volatile reaction products from the aniline or toluenediamine product. In most cases, however, vessel 10 serves as a primary catalytic reaction vessel where most of the aniline or toluenediamine product is produced. In some embodiments, vessel 10 is a fixed bed catalytic reactor, containing a suitable hydrogenation catalyst suitable for catalyzing the hydrogenation of nitrobenzene or dinitrotoluene, depending on which reactant liquid is to be hydrogenated. In some embodiments, dinitrotoluene in contact with the highly dispersed hydrogen bubbles, in the presence of a palladium catalyst, is hydrogenated to toluenediamine. In other embodiments, nitrobenzene in contact with highly dispersed hydrogen bubbles, in the presence of a suitable catalyst, is hydrogenated to aniline. Catalyst suitable for the hydrogenation of nitrobenzene includes, for example, FeCl₂ and water. In some embodiments, hydrogenation catalyst comprises finely divided nickel on diatomite. In some embodiments, the catalyst comprises a platinum-palladium catalyst on a carbon support. In some embodiments, the catalyst also includes a modifier, which in some cases comprises iron. For hydrogenation of dinitrotoluene, a palladium catalyst is used in some embodiments.

Depending on the type of catalytic reactor selected for the process, catalyst may be added continuously to vessel 10 via line 15 in some cases. Vessel/reactor 10 may be operated in either continuous or semi-continuous flow mode, or it may be operated in batch mode. The contents of vessel 10 may be maintained at a specified reaction temperature using heating and/or cooling capabilities (e.g., cooling coils) and temperature measurement instrumentation. Pressure in the vessel may be monitored using suitable pressure measurement instrumentation, and the level of reactants in the vessel may be controlled using a level regulator (not shown), employing techniques that are known to those of skill in the art. The contents are stirred continuously or semi-continuously. Without wishing to be limited by theory, it is believed that sub-micron particles or bubbles dispersed in a liquid undergo movement primarily through Brownian motion effects. The nanobubbles in the product dispersion created by HSD 40 may have greater mobility through boundary layers of solid catalyst particles, thereby facilitating and accelerating the catalytic reaction through enhanced transport of reactants.

The bulk or global operating temperature of the reactants is desirably maintained below their flash points. In some embodiments, the operating conditions of system 1 comprise a temperature in the range of from about 100° C. to about 230° C. In embodiments, the temperature is in the range of from about 160° C. to 180° C. In specific embodiments, the reaction temperature in vessel 10, in particular, is in the range of from about 155° C. to about 160° C. In some embodiments, the reaction pressure in vessel 10 is in the range of from about 203 kPa (2 atm) to about 5573 kPa-6080 kPa (55-60 atm). In some embodiments, reaction pressure is in the range of from about 811 kPa (8 atm) to about 1520 kPa (15 atm). In some embodiments, operating conditions comprise a temperature in the range of about 90° C. to about 200° C. and pressure in the range of about 100 kPa to about 600 kPa.

The hydrogenation of 1 mole of nitrobenzene produces 2 moles of water and consumes 3 moles of hydrogen for each mole of aniline produced. In vessel 10, aniline or toluenediamine production occurs via catalytic hydrogenation. The temperature of the reactants is controlled (e.g., using a heat exchanger), and the fluid level inside vessel 10 is regulated using standard techniques. The hydrogenation product may be produced either continuously, semi-continuously or batch wise, as desired for a particular application. Any reaction gas that is produced exits reactor 10 via gas line 17. This gas stream may comprise unreacted hydrogen and nitrobenzene or dinitrotoluene vapor, for example. The reaction gas removed via line 17 may be further treated, and the components may be recycled, as desired. For example, all or a portion of hydrogen-containing vent gas in line 17 may be recycled to line 13 and back into HSD 40 using a compressor type pump. In some embodiments, a portion of unreacted nitrobenzene or dinitrotoluene in vessel 10 is recycled to high shear mixer 40, via line 21, for example. Water produced during the reaction may be removed from vessel 10 prior to reuse/recycle.

The reaction product stream comprising aniline or toluenediamine, and any non-converted liquid reactant, water, solvent, and any by-products exits vessel 10 by way of at least one line 16. The aniline or toluenediamine may be recovered and treated as known to those of skill in the art, or use as a feed for further processing. For instance, toluenediamine may be further processed by reacting with phosgene gas to produce toluenediisocyanate. Aniline product may be recovered for use as a feed stock in the production of methylene diphenyl diisocyanate (MDI), which, in turn, is useful for manufacturing polyurethanes.

Multiple Pass Operation. In the embodiment shown in FIG. 1, the system is configured for single pass operation, wherein the output from vessel 10 goes directly to further processing for recovery of aniline or toluenediamine product. In some embodiments it may be desirable to pass the contents of vessel 10, or a liquid fraction containing unreacted nitrobenzene or dinitrotoluene, through HSD 40 during a second pass. In this case, line 16 may be joined to line 21, and the recycle stream from vessel 10 pumped by pump 5 into line 13 and thence into HSD 40. Additional hydrogen gas may be injected via line 22 into line 13, or it may be added directly into the high shear mixer (not shown).

Multiple High Shear Mixing Devices. In some embodiments, two or more high shear devices like HSD 40, or configured differently, are aligned in series, and are used to further enhance the reaction. Their operation may be in either batch or continuous mode. In some instances in which a single pass or “once through” process is desired, the use of multiple high shear devices in series may also be advantageous. When multiple high shear devices are operated in series, additional reactant(s) may be injected into the inlet feed stream of each device. In some embodiments, multiple high shear devices 40 are operated in parallel, and the outlet dispersions therefrom are introduced into one or more vessel 10.

The application of enhanced mixing of the reactants by HSD 40 potentially causes greater conversion of nitrobenzene to aniline, or greater conversion of dinitrotoluene to toluenediamine, in various embodiments of the method. In some embodiments, the enhanced mixing potentiates an increase in throughput of the process stream. In some embodiments, the high shear mixing device is incorporated into an established process, thereby enabling an increase in production (i.e., greater throughput). In contrast to some methods that attempt to increase the degree of conversion of nitrobenzene or dinitrotoluene by simply increasing reactor pressures, the superior dispersion and/or dissolution provided by external high shear mixing may allow in many cases a decrease in overall operating pressure while maintaining or even increasing reaction rate. Without wishing to be limited to a particular theory, it is believed that the level or degree of high shear mixing is sufficient to increase rates of mass transfer and may also produce localized non-ideal conditions that enable reactions to occur that might not otherwise be expected to occur based on Gibbs free energy predictions. Localized non-ideal conditions are believed to occur within the high shear device resulting in increased temperatures and pressures with the most significant increase believed to be in localized pressures. The increase in pressures and temperatures within the high shear device are instantaneous and localized and quickly revert back to bulk or average system conditions once exiting the high shear device. In some cases, the high shear mixing device induces cavitation of sufficient intensity to dissociate one or more of the reactants into free radicals, which may intensify a chemical reaction or allow a reaction to take place at less stringent conditions than might otherwise be required. Cavitation may also increase rates of transport processes by producing local turbulence and liquid micro-circulation (acoustic streaming). An overview of the application of cavitation phenomenon in chemical/physical processing applications is provided by Gogate et al., “Cavitation: A technology on the horizon,” Current Science 91 (No. 1): 35-46 (2006). The high shear mixing device of certain embodiments of the present system and methods is operated under what is believed to be cavitation conditions effective to dissociate the hydrogen and liquid reactants into free radicals, which then form the corresponding aniline or toluenediamine product.

Certain embodiments of the high shear method make possible a reduction in mass transfer limitations, thereby potentially increasing the reaction rate and enabling a reduction in reactor temperature, a reduction in reactor pressure, a reduction in contact time, and/or an increase in product yield. In some embodiments, the system and methods described herein make possible the design of a smaller and/or less capital intensive process than previously possible without the use of the same external high shear mixing. Potential advantages of certain embodiments of the disclosed methods are reduced operating costs and increased production from an existing process. Certain embodiments of the disclosed processes additionally offer the advantage of reduced capital costs for the design of new processes. In some embodiments, dispersing hydrogen-containing gas in solution prior to hydrogenation decreases the amount of unreacted nitrobenzene or dinitrotoluene. Potential benefits of some embodiments of this system and method for the production of aniline or toluenediamine include, but are not limited to, faster cycle times, increased throughput, higher conversion, reduced operating costs and/or reduced capital expense due to the possibility of designing smaller reactors and/or operating the process at lower temperature and/or pressure. Some embodiments of the present methods make possible an increase in the rate of a gas/liquid phase hydrogenation process for the production of toluenediamine from dinitrotoluene and hydrogen gas, or for the production of aniline from nitrobenzene and hydrogen gas, by providing for more optimal time, temperature and pressure conditions than are used in other methods. In some embodiments, such a method employs an external high shear mechanical reactor to provide enhanced time, temperature and pressure conditions resulting in accelerated chemical reactions between multiphase reactants. In still other embodiments, a high shear method uses an external pressurized high shear mixer/reactor to produce aniline or toluenediamine without the need for large volume reactors or for recovery of substantial unconverted nitrobenzene or dinitrotoluene.

While preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, and the like. Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every original claim is incorporated into the specification as an embodiment of the invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent they provide exemplary, procedural or other details supplementary to those set forth herein. 

What is claimed is:
 1. A system for production of aniline from nitrobenzene, the system comprising: at least one high shear mixing device configured for producing a dispersion of hydrogen gas bubbles in a liquid medium comprising nitrobenzene, wherein the dispersion has a mean bubble diameter of less than about 1.5 μm; a pump configured for delivering a feed comprising the liquid medium and hydrogen gas to said high shear mixing device, wherein the pump is fluidly connected to the at least one high shear mixing device via a conduit; a gas inlet line configured for introducing a dispersible gas comprising hydrogen into said conduit; and a pressure vessel configured for receiving said dispersion from said high shear mixer and comprising an outlet, and wherein the pressure vessel is configured to provide sufficient operating conditions for an exothermic catalytic reaction of nitrobenzene to form aniline.
 2. The system of claim 1 wherein said high shear mixing device comprises a rotor tip and said device is configured for operating at a flow rate of at least 300 L/h at a tip speed of at least 22.9 m/s.
 3. The system of claim 1 wherein said high shear mixing device is configured for operating at a tip speed of at least 40 m/s.
 4. The system of claim 1 further comprising a recycle line configured for recycling a fluid from the vessel to the at least one high shear mixing device.
 5. The system of claim 1 wherein the feed further comprises an alkyl monoalcohol, carbon monoxide, or both.
 6. The system of claim 5 wherein the alkyl monoalcohol is selected from the group consisting of methanol, ethyl alcohol, isopropyl alcohol, butyl alcohol, pentyl alcohol, and combinations thereof.
 7. The system of claim 1 wherein the dispersion has a mean bubble diameter of less than 400 nm.
 8. The system of claim 1 wherein the at least one high shear mixing device comprises at least one rotor and at least one complementarily-shaped stator.
 9. The system of claim 1 wherein the at least one high shear mixing device is capable of subjecting the hydrogen gas and liquid medium to a shear rate of at least 20,000s⁻¹.
 10. The system of claim 1 further comprising a hydrogenation catalyst within the vessel, the liquid medium, or both, wherein the hydrogenation catalyst is active for catalyzing the hydrogenation of nitrobenzene to aniline.
 11. The system of claim 1 wherein the vessel further comprises a vent gas line whereby gas may be removed from the vessel.
 12. The system of claim 11 further comprising a recycle line fluidly connecting the vent gas line with the at least one high shear mixing device.
 13. The system of claim 12 further comprising a pump on the recycle line.
 14. The system of claim 1 further comprising apparatus for removing from the product at least one component selected from the group consisting of nitrobenzene, liquid medium, and water and other by-products of aniline production.
 15. The system of claim 1 wherein said conduit is configured to convey the feed comprising liquid medium and hydrogen.
 16. The system of claim 4 wherein the recycle line is configured to recycle a fluid comprising unreacted nitrobenzene from the vessel to the pump.
 17. The system of claim 4 wherein the recycle line connects the vessel with the conduit.
 18. The system of claim 10 wherein the hydrogenation catalyst comprises a metallic catalyst.
 19. The system of claim 18 wherein the metallic catalyst comprises at least one component selected from the group consisting of ferrous chloride, iron, palladium, platinum and nickel.
 20. The system of claim 12 wherein the gas comprises at least one component selected from the group consisting of unreacted nitrobenzene and hydrogen.
 21. The system of claim 1, wherein the pressure vessel is configured to provide an operable reaction pressure of between the range of about 150 kPa and 6080 kPa.
 22. The system of claim 21, wherein the pressure vessel is configured to provide an operable reaction pressure of between the range of about 811 kPa and 1520 kPa. 